Simplified fiber tensioning for automated fiber placement machines

ABSTRACT

A fiber tensioning device is provided for a spool of fibers. A hub is rotatably mounted on the support and is adapted to have the spool of fibers mounted thereon. Means on the hub apply a drag force on fibers being drawn from the spool to maintain the fibers in tension.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. patent application Ser. No. 12/038,155, filed on Feb. 27, 2008, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure generally relates to automated fiber placement machines, especially those used to layup composite structures, and deals more particularly with a simplified fiber tensioning system.

BACKGROUND

Composite structures such as those used in the automotive, marine and aerospace industries may be fabricated using automated composite material application machines, commonly referred to as automated fiber placement (AFP) machines. AFP machines may be used in the aircraft industry, for example to fabricate structural shapes and skin assemblies by wrapping relatively narrow strips of composite, slit fiber tape or “tows” around a manufacturing tool. The AFP machine aligns and places a plurality of the tape strips, typically six or more, in continuous, edge-to-edge contact forming a single wide, conformal bandwidth which is placed on and compacted against the tool.

In the past, AFP machines have been relatively large and complex in order to provide features and functions that allow them to fabricate a wide range of large scale structures. During tape placement, the fiber tape is drawn from spools of the tape mounted on the machine. It is necessary to maintain a proper amount of tension on the fiber tape as it is drawn from the spools, and to compensate for slack in the tape which may occur during normal AFP machine operation. Tensioning of the fiber tape is controlled by a relatively complicated feedback system that employs a looped network of servo motor drives and sensor arrays. Other tensioning systems have employed a rotational drag brake and release mechanism combined with external torsion spring biased rollers to compensate for variations in tape slack.

More recently, smaller, simplified AFP machines have been proposed that are capable of placing narrower fiber tows, and are therefore may be better suited for fabricating smaller structures and components. Although the mechanisms used in the fiber placement heads of these simplified AFP machines are smaller and have reduced complexity, the machines nevertheless utilize standard size spools of composite fiber tape of the type discussed above. The use of known, relatively complicated fiber tensioning systems may not be compatible with these smaller AFP machines.

Accordingly, there is a need for a simplified fiber tensioning device that may be used with simplified AFP machines using standard size spools of tape.

SUMMARY

According to the disclosed embodiments, a simplified device is provided for maintaining fiber tension and for compensating for fiber slack in fiber placement machines. The device allows compact packaging of multiple standard size spools of composite fibers on an AFP head which provides fiber tensioning and slack compensation within each independent hub upon which a spool is mounted.

According to one embodiment, a fiber tensioning device is provided for use with a spool of fiber from which fibers are drawn. A hub is rotatably mounted on a support and is adapted to have a spool of fibers mounted thereon for rotation on the support. Means on the hub apply drag force on the fibers being drawn from the spool in order to maintain tension on the fibers. The means for applying drag force may include biasing means for applying a force to the hub in a direction resulting in drag force being applied to the fibers drawn from the spool, and means for limiting the rotational force applied to the hub by the spring. The means for limiting the rotational force may include a clutch which includes a clutch disc and a friction pad frictionally engaging the clutch disc.

According to another embodiment, a device for maintaining tension on fiber drawn from a spool may be used with an automatic fiber placement system having at least one supply spool of fibers. The device includes a rotatable hub adapted to have a supply spool mounted thereon for rotation for the hub. Means are provided in the hub for applying a rotational force on the hub opposing a force applied thereon by fibers being drawn from the spool.

According to a further embodiment, a method is provided of maintaining tension on fibers being drawn from a fiber supply spool in an automatic fiber placement system. The method includes placing the spool on a hub, and using a spring to apply a rotational force to the hub that maintains tension on the fibers being drawn from the spool. The method may further comprise using a clutch inside the hub to limit the amount if force applied to the hub by the spring. The clutch may be selectively disengaged to reduce the tension on the fibers being drawn from the spool.

The disclosed embodiments satisfy the need for a simplified device for tensioning fibers and compensating for fiber slack in a simplified, smaller automatic fiber placement machine employing standard size spools of fiber tape.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is an illustration of a functional block diagram of a simplified fiber tensioning device according to the disclosed embodiments.

FIG. 2 is an illustration of a flow diagram showing the overall steps of a method for maintaining tension on fibers being drawn from a supply spool.

FIG. 3 is an illustration of a side view of a reduced complexity fiber placement head employing standard size spools of fibers and a simplified fiber tensioning device.

FIG. 4 is an illustration of a diagrammatic, perspective view of one of the spools shown in FIG. 3, mounted on a hub.

FIG. 5 is an illustration of a longitudinal sectional view of the hub shown in FIG. 4.

FIG. 6 is an illustration of an end view of the hub shown in FIG. 5.

FIG. 7 is an illustration of an exploded, perspective view of the hub shown in FIGS. 5 and 6.

FIG. 8 is an illustration of a sectional view of the clutch disengagement device, showing the clutch in its engaged position.

FIG. 9 is an illustration of a sectional view similar to FIG. 8 but showing the disengagement device having disengaged the clutch.

FIG. 10 is an illustration of a flow diagram of aircraft production and service methodology.

FIG. 11 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIG. 1, the disclosed embodiments generally relate to a device 20 used to apply tension in fibers and compensate for fiber slack in an automatic fiber placement (AFP) head 46. The device 20 includes a hub 22 containing biasing means in the form of a torsion spring 24 which is connected to the hub 22 through a clutch 26 which limits the amount of force applied to the hub 22 by the spring 24. The device 20 may optionally include a clutch disengagement device 28 which selectively disengages the clutch 26 in order to suspend the tension applied to the hub 22 by the torsion spring 20. A supply spool 30 of fibers is mounted on the hub 22 and the combination of the hub 22 and the supply spool 30 are mounted on a support 32 forming part of the AFP head 46.

FIG. 2 broadly illustrates the steps of a method of using the device 22 to apply tension in fibers being drawn from the supply spool 30 during an ordinary fiber placement operation performed by the AFP head 46. Beginning at 34, the supply spool 30 is placed on the hub 22. A spring 24 is placed inside the hub 22 at 35. At 36, the torsion spring 24 is connected between the hub 22 and the support 32. At 38, the torsion spring 24 is used to apply tension to the hub 22. Finally, at 40, the clutch 26 may be used to suspend the tension being applied to the hub 22 by the spring 24.

Attention is now directed to FIGS. 3 and 4 which illustrate further details of the AFP head 42 and supply spools 30. The head 42 may include a frame 46 on which there is mounted one or more supply spools 30 of fibers 50. As used herein, “fiber” and “fibers” refers to composite fibers that may be in the form of composite fiber tape that may be cut into narrow strips which are sometimes referred to as tows, as well as to fiber rovings. Although two supply spools 30 are shown in the drawings, more or less than two spools may be present on the head 42. Each of the supply spools 30 is removably supported on a hub 22 for rotation therewith, and feeds fibers 50 to one or more fiber alignment and re-thread mechanisms 44. The mechanisms guide the fibers 50 into aligned, side-by-side relationship to form a bandwidth 55 which may be cut by a mechanism 44 and compacted onto a substrate 54 by a compaction roller 52.

Attention is now directed to FIGS. 5, 6 and 7 which illustrate further details of the device 20. The hub 22 is generally cylindrical in shape and includes an essentially open interior 23. A shaft 32 fixed on the frame 46 extends longitudinally through the center of the hub 22 and provides a means for supporting both the hub 22 and the supply spool 30 on the head 42. The hub 22 is rotatably mounted on the shaft 32 by means of a pair of bearings 56 and 60.

A helical torsion spring 24 is sleeved over the shaft 32 inside the hub 22 and has one end 27 thereof fixed to the shaft 32 so that end 27 remains stationary. The opposite end 29 of the torsion spring 24 is fixed to a clutch disc 26 a forming part of a clutch 26 that includes friction pads 26 b fixed on the hub 22. The spring 24 is compressed between ends 27 and 29 and therefore generates a compressive force that biases the clutch disc 26 a in the direction shown by the frictional drag 21 into frictional engagement with the friction pads 26 b which may rotate along with the hub 22. Initial rotation of the hub 22 results in winding up the torsion spring 24 until the angular torsion force applied to the clutch disc 26 a by the spring 24 in the direction shown by the arrow 31 (FIG. 6) overcomes the friction between the clutch disc 26 a and the pads 26 b, at which point the clutch disc 26 a slips relative to the pads 26 b as the pads 26 b continue to turn.

As hub 22 rotates on shaft 32, the clutch disc 26 a frictionally engages the pads 26 b to produce frictional drag on hub 22 shown by the arrow 31 in FIG. 6, in turn applying tension to fibers 50 being drawn off the supply spool 30. The spring 24 is maintained concentric with the shaft 32 by a bearing 58 and the end of 29 of the spring 24 that is fixed to the clutch disc 26 a. The clutch 26 limits the amount of torsional force applied by the spring 24 to the hub 22. The frictional drag applied by the spring 24 through the clutch 26 to the hub 22 determines the amount of tension force applied to the fibers 50 being drawn from the supply spool 22. Although not shown in FIGS. 5 and 6, a clutch disengagement device 28 discussed below and shown in FIGS. 7-9, allows disengagement of the clutch disc 26 a from the friction pads 26 b.

Referring particularly to FIG. 6 as the fibers 50 are slowly drawn from the spool 22, the spring 24 begins to wind from position A₀ to position A₁ through an angle β. During angular rotation through β, the clutch disc 26 a rotates along with the friction pads 26 b. However when the rotation of the spool 22 advances to the position shown as A2, the rotational force applied to the clutch disc 26 a by the spring 24 shown by the frictional drag 31 overcomes the friction 33 between the clutch disc 26 a, and the friction pads 26 b thus allowing the clutch disc 26 a to slip in the direction 31 relative to the pads 26 b.

Angular displacement of the spool 22 through the angle β allows the fibers to advance to position P₁. The advancement of the fibers 50 to point P₂ corresponds to the angular displacement at A₂ where the clutch disc 26 a begins to slip. When the fibers 50 advance from P₁ to P₂, the force F applied to the fibers 50 will be equal to the rotational restraining moment between the clutch disc 26 a and the compressive force applied by the spring 24 to the clutch disc 26 a. In the event that the advancement of the fibers 50 is stopped and retracted from position P₂ to position P₁, the resulting slack in the fibers 50 is taken up by the torsion spring 24.

Referring now also to FIGS. 7-9, a cylindrically shaped clutch deactivation device 28 may be optionally provided in order to disengage the clutch 26 where it is desired, for example to reduce the drag force on the fibers 50 during start-up of the head 42, or when the placement of a new tape bandwidth 55 is about to be commenced. As best seen in FIG. 8, the clutch deactivation device 28 is generally cylindrical in shape and includes an end wall 28 a disposed outside of the hub 22. The sides 28 b of the device 28 slide through the hub 22 so that the end 28 c of the device 28 may engage the periphery of the clutch disc 26 a. Thus, by sliding the device 28 axially 37 into the hub 22, the force applied to the clutch disc 26 a by the spring 24 is overcome, allowing the clutch disc 26 a to be displaced along the shaft 32 a distance “D” (FIG. 9), which in turn disengages the clutch disc 26 a from the friction pads 26 b. Due to the spring loading provided by spring 24, releasing the device 28 results in the spring 24 forcing the clutch disc 26 a back into frictional engagement with the friction pads 28 b.

Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine and automotive applications. Thus, referring now to FIGS. 10 and 11, embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method 62 as shown in FIG. 10 and an aircraft 64 as shown in FIG. 11. During pre-production, exemplary method 62 may include specification and design 66 of the aircraft 64 and material procurement 68. During production, component and subassembly manufacturing 70 and system integration 72 of the aircraft 62 takes place. The simplified tensioning device 20 may be used in an AFP machine employed to fabricate composite structures forming components or subassemblies that are assembled at 70 or integrated as part of a system at 72. Thereafter, the aircraft 64 may go through certification and delivery 56 in order to be placed in service 76. While in service by a customer, the aircraft 64 is scheduled for routine maintenance and service 78 (which may also include modification, reconfiguration, refurbishment, and so on). The simplified tensioning device may be used in an AFP machine employed to fabricate replacement parts or components used in the maintenance and service 78.

Each of the processes of method 62 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.

As shown in FIG. 11, the aircraft 64 produced by exemplary method 62 may include an airframe 80 with a plurality of systems 82 and an interior 84. Examples of high-level systems 82 include one or more of a propulsion system 86, an electrical system 88, a hydraulic system 90, and an environmental system 92. Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries.

Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method 62. For example, components or subassemblies corresponding to production process 70 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 64 is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 70 and 72, for example, by substantially expediting assembly of or reducing the cost of an aircraft 64. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft 64 is in service, for example and without limitation, to maintenance and service 78.

Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art. 

1. A fiber tensioning device for use with a spool of fiber from which fibers are drawn, comprising: a support; a hub rotatably mounted on the support, the hub being adapted to have the spool of fibers mounted thereon for rotation therewith on the support, said hub rotatably mounted for rotation around a shaft, said shaft stationary with respect to rotation of said hub around said shaft; and means for applying drag force on fibers being drawn from the spool, said means for applying drag force being located on the hub and comprising biasing means wherein a portion of said biasing means is fixed to said shaft.
 2. The device of claim 1, wherein the means for applying drag force includes: said biasing means for biasing the hub in a direction resulting in the drag force being applied to the fibers drawn from the spool; and means for limiting the drag force applied to the hub by the biasing means.
 3. The device of claim 1 wherein: the biasing means includes a spring mounted between the hub and the shaft.
 4. The device of claim 3, wherein the spring is sleeved over the shaft.
 5. The device of claim 2, wherein the means for limiting the drag force includes a slip clutch.
 6. The device of claim 5, wherein the clutch includes: a clutch disc, and a friction pad frictionally engaging the clutch disc.
 7. The device of claim 6, wherein: the biasing means includes a spring, the clutch disc is connected to the spring, and the friction pad is mounted on the hub.
 8. The device of claim 5, further comprising: means on the hub for disengaging the clutch.
 9. For use with an automatic fiber placement system having at least one supply spool of fibers, a fiber tensioning device for maintaining tension on fibers drawn from the spool, comprising: a rotatable hub adapted to have the supply spool mounted thereon for rotation with the hub, said hub rotatably mounted for rotation around a shaft, said shaft stationary with respect to rotation of said hub around said shaft; and means for applying a rotational force on the hub opposing a force applied to the hub by fibers being drawn from the spool, said means for applying said rotational force being located on the hub and comprising biasing means wherein a portion of said biasing means is fixed to said shaft.
 10. The device of claim 9, wherein the biasing means includes a spring.
 11. The device of claim 9, further comprising: means for limiting the force applied to the hub by the means for applying the rotational force, wherein said means for limiting the force is located on the hub.
 12. The device of claim 11, wherein the means for limiting the force applied to the hub includes a slip clutch.
 13. The device of claim 12, wherein the clutch includes: a clutch disc, and a clutch pad frictionally engaging the clutch disc.
 14. The device of claim 12, further comprising: means for disengaging the clutch.
 15. A method of maintaining tension on fibers being drawn from a fiber supply spool on an automatic fiber placement machine, comprising: placing the spool on a hub; and using a spring within the hub to apply a rotational force to the hub that maintains tension on the fibers being drawn from the spool, said hub rotatably mounted for rotation around a shaft, said shaft stationary with respect to rotation of said hub around said shaft, a portion of said spring fixed to said shaft.
 16. The method of claim 15, further comprising: using a slip clutch within the hub to limit the rotational force applied to the hub by the spring.
 17. The method of claim 16, further comprising: selectively disengaging the clutch to reduce the tension on the fibers being drawn from the spool.
 18. The method of claim 17, wherein selectively disengaging the clutch is performed by displacing a clutch disengagement device on the hub.
 19. For use with an automatic fiber placement system having at least one supply spool of fibers, a fiber tensioning device for maintaining tension on fibers drawn from the spool, comprising: a shaft; a hub adapted to have the spool mounted thereon; means including bearings for mounting the hub for rotation around the shaft, said shaft stationary with respect to rotation of said hub around said shaft; a spring sleeved over the shaft inside the hub, the spring having a first end secured to the shaft and having a second end; a slip clutch within the hub and coupled between the second end of the spring and the hub; and means on the hub for disengaging the clutch.
 20. A method of maintaining tension on fibers being drawn from a fiber supply spool in an automatic fiber placement system, comprising: placing the spool on a hub, said hub rotatably mounted for rotation around a shaft, said shaft stationary with respect to rotation of said hub around said shaft, a spring sleeved over said shaft and comprising a first end fixed to said shaft; connecting a second end of said spring with the hub through a slip clutch; using the spring to apply a rotational force to the hub keeping the fibers in tension; using the clutch to limit the rotational force applied to the hub by the spring; placing a clutch disengagement device on the hub; and using the clutch disengagement device to selectively disengage the spring from the hub. 